1. Field of the Invention
The invention pertains to a vibration damper including a cylinder filled with a working medium, the cylinder being fitted with a piston rod guide; a piston rod and a piston installed in the cylinder with freedom of axial movement, the piston dividing the cylinder into a working space on the piston rod side and a working space away from the piston rod; and means for limiting the outward movement of the piston rod in the event of a fire.
2. Description of the Related Art
A fire safety device for a vibration damper is known from U.S. Pat. No. 5,454,455. It consists of beads on the cylinder, against which the piston can be supported. This principle works as desired in conventional pistons with a piston ring inside a piston ring groove. In the event of a fire, the piston makes contact with a bead, at least one of which is provided. This contact forces the piston rod guide to assume a slanted position, which prevents both the piston rod and the piston rod guide from being ejected suddenly from the pre-pressurized cylinder.
A piston for a vibration damper is known by way of example from U.S. Pat. No. 5,615,756; the piston ring of this piston is relatively thick, because it is designed to rest against both the top and bottom of the piston. In a piston ring-piston design of this type, the piston ring can lose its shape during a fire, and thus the piston will not be held by the beads; that is, the piston rod guide will not assume a slanted position. The overall result is that the fire safety measure does not go into effect as planned.
A proposed remedy is to impress the beads in the special way described in U.S. Pat. No. 6,153,285. These especially deep beads, however, require that the cylinder be made of a material which can be shaped in the desired way without cracking. In addition, the flow-through cross sections in the piston are always made larger, which has the effect of decreasing the load-bearing capacity of the piston.